Merge dynamic-schema-generation into master

cmd/dgraph/main.go

cmd/dgraph/main_test.go

gql/parser.go

posting/index.go

posting/list.go

query/graph/graphresponse.pb.go

query/graph/graphresponse.proto

query/outputnode.go

query/query.go

rdf/parse.go

rdf/parse_test.go

schema/parse.go

schema/parse_test.go

schema/schema.go

types/conversion.go

types/conversion_test.go

types/scalar_types.go

types/types.pb.go

types/types.proto

worker/backup.go